Alkaline earth metals are elements that belong to the second group of the periodic table. These include substances such as calcium, magnesium, barium, beryllium, strontium and radium. The name of this group indicates that in water they give an alkaline reaction.
Alkali and alkaline earth metals, or rather their salts, are widely distributed in nature. They are represented by minerals. The exception is radium, which is considered a fairly rare element.
All of the above metals have some common qualities, which made it possible to combine them into one group.
Alkaline earth metals and their physical properties
Almost all of these elements are grayish solids (at least under normal conditions and by the way, the physical properties are slightly different - these substances, although quite persistent, are easily affected.
Interestingly, with the serial number in the table, such an indicator of the metal as density also grows. For example, in this group, calcium has the lowest index, while radium is similar in density to iron.
Alkaline earth metals: chemical properties
To begin with, it is worth noting that the chemical activity increases according to the serial number of the periodic table. For example, beryllium is a fairly stable element. It reacts with oxygen and halogens only when heated strongly. The same goes for magnesium. But calcium is able to slowly oxidize even at room temperature. The remaining three representatives of the group (radium, barium and strontium) quickly react with atmospheric oxygen even at room temperature. That is why these elements are stored, covering with a layer of kerosene.
The activity of oxides and hydroxides of these metals increases in the same way. For example, beryllium hydroxide does not dissolve in water and is considered an amphoteric substance, but is considered a fairly strong alkali.
Alkaline earth metals and their brief characteristics
Beryllium is a light gray hard metal with high toxicity. The element was first discovered in 1798 by the chemist Vauquelin. There are several minerals of beryllium in nature, of which the following are considered the most famous: beryl, phenakite, danalite and chrysoberyl. By the way, some beryllium isotopes are highly radioactive.
Interestingly, some forms of beryl are valuable gemstones. These include emerald, aquamarine and heliodor.
Beryllium is used to make some alloys. This element is used to slow down neutrons.
Calcium is one of the best known alkaline earth metals. In its pure form, it is a soft white substance with a silvery tint. Pure calcium was first isolated in 1808. In nature, this element is present in the form of minerals such as marble, limestone and gypsum. Calcium is widely used in modern technologies. It is used as a chemical fuel source and also as a fire retardant material. It's no secret that calcium compounds are used in the production of building materials and medicines.
This element is also found in every living organism. Basically, he is responsible for the operation of the motor apparatus.
Magnesium is a light and fairly malleable metal with a characteristic grayish color. It was isolated in its pure form in 1808, but its salts became known much earlier. Magnesium is found in minerals such as magnesite, dolomite, carnallite, kieserite. By the way, magnesium salt provides a huge number of compounds of this substance can be found in sea water.
Properties of elements of II A group.
|
Properties |
4Be |
12Mg |
20Ca |
38Sr |
56Ba |
88Ra |
|
Atomic mass |
9,012 |
24,305 |
40,80 |
87,62 |
137,34 |
226,025 |
|
Electronic configuration* |
||||||
|
0,113 |
0,160 |
0,190 |
0,213 |
0,225 |
0,235 |
|
|
0,034 |
0,078 |
0,106 |
0,127 |
0,133 |
0,144 |
|
|
Ionization energy |
9,32 |
7,644 |
6,111 |
5,692 |
5,21 |
5,28 |
|
Relative electro- |
1,5 |
1,2 |
1,0 |
1,0 |
0,9 |
0,9 |
|
Possible oxidation states |
||||||
|
clarke, at.% (distribu- |
1*10 -3 |
1,4 |
1,5 |
8*10 -3 |
5*10 -3 |
8*10 -12 |
|
State of aggregation (Well.). |
S E R D E S E S T V A |
|||||
|
Color |
Gray |
Silver |
S E R E B R I S T O - WHITE |
|||
|
1283 |
649,5 |
850 |
770 |
710 |
700 |
|
|
2970 |
1120 |
1487 |
1367 |
1637 |
1140 |
|
|
Density |
1,86 |
1,741 |
1,540 |
2,67 |
3,67 |
|
|
Standard electrode potential |
1,73 |
2,34 |
2,83 |
2,87 |
2,92 |
|
*The configurations of the external electronic levels of atoms of the corresponding elements are given. The configurations of the remaining electronic levels coincide with those for the noble gases that complete the previous period and are indicated in parentheses.
As follows from the data given in the table, the elements of group IIA have low (but still not the lowest: compare with IA gr.) ionization energy and relative electronegativity, and these values decrease from Be to Ba, which allows us to conclude that that these elements are typical reducing metals, and Ba is more active than Be.
Ve - exhibits, like aluminum, amphoteric properties. However, in Be, the metallic properties are still more pronounced than the non-metallic ones. Beryllium reacts, unlike the other elements of group IIA, with alkalis.
Chemical bonds in Be compounds are mainly covalent, while bonds in compounds of all other elements (Mg - Ra) are ionic in nature. At the same time, as with group IA elements, bonds with halogens and oxygen are very strong, and with hydrogen, carbon, nitrogen, phosphorus and sulfur they are easily hydrolyzed.
physical properties. These are silver-white metals, relatively light, soft (with the exception of beryllium), ductile, fusible (everything except beryllium), have good electrical and thermal conductivity.
Practical use. Be is used in nuclear technology as a neutron moderator and absorber. Alloys of beryllium with copper - bronze - are very resistant, and with nickel - they have high chemical resistance, due to which they are used in surgery.
Mg, Ca - are used as good reducing agents in metallothermy.
Ca, Sr, Ba - react quite easily with gases and are used as getters (absorbers from the air) in vacuum technology.
Receipt. Being highly reactive, alkaline earth metals do not occur in nature in a free state, they are obtained by electrolysis of halide melts or by metallothermy. In nature, alkaline earth elements are part of the following minerals: -beryl; - feldspar; - bischofite - used in medicine and to obtain magnesium by electrolysis. To obtain beryllium in metallurgy, fluoroberyllates are used: .
Chemical properties. Alkaline earth metals easily react with oxygen, halogens, non-metals, water and acids, especially when heated:
This reaction is especially easy for calcium and barium, so they are stored under special conditions.
Barium persulfide BaS is a phosphor.
Hydrolysis of acetylenides produces acetylene:
It was not possible to obtain compounds of Be and Mg with hydrogen by direct interaction of simple substances: the reaction does not go whereas goes pretty easy. The resulting hydrides are strong reducing agents. passivation, no reaction
Oxides of alkaline earth metals. Oxides of alkaline earth elements are widely used in construction. They are obtained by decomposition of salts: - CaO - quicklime.
In the series of oxides from BeO to BaO from left to right, the solubility of oxides in water, their main properties and chemical activity increase, as follows: BeO is insoluble in water, amphoterene, MgO is slightly soluble in water, and CaO, SrO, BaO are highly soluble in water with the formation of hydroxides Me (OH) : .
The melting points of oxides decrease in the series BeO ® BaO. Melting points of oxides BeO and MgO » 2500 ° C, which allows them to be used as refractory materials.
Hydroxides of alkaline earth metals. In the series Be (OH) 2 ® Ba (OH) 2, the radius of Me 2+ ions increases, and, as a result, the probability of manifestation of the main properties of hydroxides, their solubility in water increases: Be (OH) 2 - is slightly soluble in water, due to its amphoteric exhibits weak acidic and basic properties, and Ba (OH) 2 is highly soluble in water and can be compared in strength with such a strong base as NaOH.
The amphotericity of beryllium hydroxide can be illustrated by the following reactions:
Salts of alkaline earth metals. Soluble salts Be and Ba - toxic, poisonous! CaF 2- sparingly soluble salt, occurs in nature as fluorite or fluorspar, is used in optics. CaCl 2 , MgCl 2- highly soluble in water, are used in medicine and chemical synthesis as desiccants. Carbonates are also widely used in construction: CaCO 3H MgCO 3- dolomite - used in construction and to obtain Vg and Ca. CaCO 3 - calcite, chalk, marble, Icelandic spar, MgCO 3- magnesite. The content of soluble carbonates in natural water determines its hardness: . Sulfates are also widespread natural compounds of alkaline earth metals: CaSO 4H 2H 2 O- gypsum - widely used in construction. MgSO 4H 7H 2 O- epsomite, "English bitter salt", BaSO 4- finds application with fluoroscopy. Phosphates: Ca 3 (RO 4) 2- phosphorite, Ca (H 2 RO 4) 2, CaHRO 4- precipitate - used for the production of fertilizers, Ca 5 (RO 4) 3H (OH -, F -, Cl -) - appatite - natural mineral Ca, NH 4 Mg (PO 4)- slightly soluble compound. Other salts are also known: Ca (NO 3) 2H 2H 2 O- Norwegian saltpeter, Mg(ClO 4) 2- Anhydrone is a very good desiccant.
Group IIA contains only metals - Be (beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium) and Ra (radium). The chemical properties of the first representative of this group, beryllium, differ most strongly from the chemical properties of the other elements of this group. Its chemical properties are in many ways even more similar to aluminum than to other Group IIA metals (the so-called "diagonal similarity"). Magnesium also differs markedly from Ca, Sr, Ba and Ra in chemical properties, but still has much more similar chemical properties with them than with beryllium. Due to the significant similarity of the chemical properties of calcium, strontium, barium and radium, they are combined into one family, called alkaline earth metals.
All elements of group IIA belong to s-elements, i.e. contain all of their valence electrons s-sublevel. Thus, the electronic configuration of the outer electron layer of all chemical elements of this group has the form ns 2 , Where n– number of the period in which the element is located.
Due to the peculiarities of the electronic structure of group IIA metals, these elements, in addition to zero, are capable of having only one single oxidation state, equal to +2. Simple substances formed by elements of group IIA, when participating in any chemical reactions, can only be oxidized, i.e. donate electrons:
Me 0 - 2e - → Me +2
Calcium, strontium, barium and radium are extremely reactive. The simple substances formed by them are very strong reducing agents. Magnesium is also a strong reducing agent. The reducing activity of metals obeys the general laws of the periodic law of D.I. Mendeleev and increases down the subgroup.
Interaction with simple substances
with oxygen
Without heating, beryllium and magnesium do not react with either atmospheric oxygen or pure oxygen due to the fact that they are covered with thin protective films consisting of BeO and MgO oxides, respectively. Their storage does not require any special methods of protection from air and moisture, unlike alkaline earth metals, which are stored under a layer of a liquid inert to them, most often kerosene.
Be, Mg, Ca, Sr, when burned in oxygen, form oxides of the composition MeO, and Ba - a mixture of barium oxide (BaO) and barium peroxide (BaO 2):
2Mg + O 2 \u003d 2MgO
2Ca + O 2 \u003d 2CaO
2Ba + O 2 \u003d 2BaO
Ba + O 2 \u003d BaO 2
It should be noted that during the combustion of alkaline earth metals and magnesium in air, the reaction of these metals with atmospheric nitrogen also proceeds side by side, as a result of which, in addition to compounds of metals with oxygen, nitrides with the general formula Me 3 N 2 are also formed.
with halogens
Beryllium reacts with halogens only at high temperatures, while the rest of the Group IIA metals already at room temperature:
Mg + I 2 \u003d MgI 2 - magnesium iodide
Ca + Br 2 \u003d CaBr 2 - calcium bromide
Ba + Cl 2 \u003d BaCl 2 - barium chloride
with non-metals of IV–VI groups
All metals of group IIA react when heated with all non-metals of groups IV-VI, but depending on the position of the metal in the group, as well as the activity of non-metals, a different degree of heating is required. Since beryllium is the most chemically inert among all metals of group IIA, its reactions with nonmetals require significantly more O high temperature.
It should be noted that the reaction of metals with carbon can form carbides of various nature. There are carbides related to methanides and conventionally considered derivatives of methane, in which all hydrogen atoms are replaced by a metal. They, like methane, contain carbon in the -4 oxidation state, and during their hydrolysis or interaction with non-oxidizing acids, methane is one of the products. There is also another type of carbides - acetylenides, which contain the C 2 2- ion, which is actually a fragment of the acetylene molecule. Carbides of the acetylenide type upon hydrolysis or interaction with non-oxidizing acids form acetylene as one of the reaction products. What type of carbide - methanide or acetylenide - will be obtained by the interaction of one or another metal with carbon depends on the size of the metal cation. As a rule, methanides are formed with metal ions having a small radius, and acetylides with larger ions. In the case of metals of the second group, methanide is obtained by the interaction of beryllium with carbon:
The remaining metals of group II A form acetylenides with carbon:
With silicon, group IIA metals form silicides - compounds of the Me 2 Si type, with nitrogen - nitrides (Me 3 N 2), phosphorus - phosphides (Me 3 P 2):
with hydrogen
All alkaline earth metals react when heated with hydrogen. In order for magnesium to react with hydrogen, heating alone, as in the case of alkaline earth metals, is not enough; in addition to high temperature, an increased pressure of hydrogen is also required. Beryllium does not react with hydrogen under any conditions.
Interaction with complex substances
with water
All alkaline earth metals actively react with water to form alkalis (soluble metal hydroxides) and hydrogen. Magnesium reacts with water only during boiling, due to the fact that when heated, the protective oxide film of MgO dissolves in water. In the case of beryllium, the protective oxide film is very resistant: water does not react with it either when boiling or even at a red heat temperature:
with non-oxidizing acids
All metals of the main subgroup of group II react with non-oxidizing acids, since they are in the activity series to the left of hydrogen. In this case, a salt of the corresponding acid and hydrogen are formed. Reaction examples:
Be + H 2 SO 4 (razb.) \u003d BeSO 4 + H 2
Mg + 2HBr \u003d MgBr 2 + H 2
Ca + 2CH 3 COOH = (CH 3 COO) 2 Ca + H 2
with oxidizing acids
− dilute nitric acid
All Group IIA metals react with dilute nitric acid. In this case, the reduction products instead of hydrogen (as in the case of non-oxidizing acids) are nitrogen oxides, mainly nitrogen oxide (I) (N 2 O), and in the case of highly dilute nitric acid, ammonium nitrate (NH 4 NO 3):
4Ca + 10HNO 3 ( razb .) \u003d 4Ca (NO 3) 2 + N 2 O + 5H 2 O
4Mg + 10HNO3 (very disaggregated)\u003d 4Mg (NO 3) 2 + NH 4 NO 3 + 3H 2 O
− concentrated nitric acid
Concentrated nitric acid at ordinary (or low) temperature passivates beryllium, i.e. does not react with it. When boiling, the reaction is possible and proceeds mainly in accordance with the equation:
Magnesium and alkaline earth metals react with concentrated nitric acid to form a wide range of different nitrogen reduction products.
− concentrated sulfuric acid
Beryllium is passivated with concentrated sulfuric acid, i.e. does not react with it under normal conditions, however, the reaction proceeds during boiling and leads to the formation of beryllium sulfate, sulfur dioxide and water:
Be + 2H 2 SO 4 → BeSO 4 + SO 2 + 2H 2 O
Barium is also passivated by concentrated sulfuric acid due to the formation of insoluble barium sulfate, but reacts with it when heated, barium sulfate dissolves when heated in concentrated sulfuric acid due to its conversion to barium hydrogen sulfate.
The remaining metals of the main group IIA react with concentrated sulfuric acid under any conditions, including in the cold. Sulfur reduction can occur to SO 2, H 2 S and S, depending on the activity of the metal, the reaction temperature and the concentration of the acid:
Mg + H 2 SO 4 ( conc .) \u003d MgSO 4 + SO 2 + H 2 O
3Mg + 4H2SO4 ( conc .) \u003d 3MgSO 4 + S↓ + 4H 2 O
4Ca + 5H2SO4 ( conc .) \u003d 4CaSO 4 + H 2 S + 4H 2 O
with alkalis
Magnesium and alkaline earth metals do not interact with alkalis, and beryllium easily reacts both with alkali solutions and with anhydrous alkalis during fusion. Moreover, when the reaction is carried out in an aqueous solution, water also participates in the reaction, and the products are tetrahydroxoberyllates of alkali or alkaline earth metals and gaseous hydrogen:
Be + 2KOH + 2H 2 O \u003d H 2 + K 2 - potassium tetrahydroxoberyllate
When carrying out the reaction with solid alkali during fusion, beryllates of alkali or alkaline earth metals and hydrogen are formed.
Be + 2KOH \u003d H 2 + K 2 BeO 2 - potassium beryllate
with oxides
Alkaline earth metals, as well as magnesium, can reduce less active metals and some non-metals from their oxides when heated, for example:
The method of restoring metals from their oxides with magnesium is called magnesiumthermy.
Distribution in nature and obtaining. Magnesium and calcium are common elements on Earth (magnesium is the eighth, calcium is the sixth), and the rest of the elements are rarer. Strontium and radium are radioactive elements.
In the earth's crust beryllium is in the form of minerals: beryl Be 3 Al 2 (Si0 3) 6, phenakite Be 2 Si0 4 . Impurity-colored transparent varieties of beryl (green emeralds, blue aquamarines etc.) - precious stones. 54 actually beryllium minerals are known, the most important of them is beryl (and its varieties - emerald, aquamarine, heliodor, sparrowite, rosterite, bazzite).
Magnesium is a part of silicate (among them predominates olivine Mg 2 Si0 4), carbonate ( dolomite CaMg(C0 3) 2 , magnesite MgC0 3) and chloride minerals ( carnallite KClMgCl 2 -6H 2 0). A large amount of magnesium is found in sea water (up to 0.38% MgCl 2) and in the water of some lakes (up to 30% MgCl 2).
Calcium contained in the form of silicates and aluminosilicates in rocks (granites, gneisses, etc.), carbonate in the form calcite CaCO 3, mixtures of calcite and dolomite (marble), sulfate (anhydrite CaS0 4 and gypsum CaS0 4 -2H 2 0) as well as fluoride (fluorite CaF 2) and phosphate (apatite Ca 5 (P0 4) 3), etc.
Essential Minerals strontium And barium: carbonates (strontianite SrC0 3 , witherite BaCO 3) and sulfates (celestine SrS0 4 , barite BaSO 4). Radium found in uranium ores.
In industry beryllium, magnesium, calcium, strontium and barium receive:
- 1) electrolysis of melts of MeCl 2 chlorides, to which NaCl or other chlorides are added to lower the melting point;
- 2) metal- and coal-thermal methods at temperatures of 1000-1300°C.
Particularly pure beryllium is obtained by zone melting. To obtain pure magnesium (99.999% Mg), technical magnesium is repeatedly sublimated in a vacuum. Barium of high purity is obtained by the aluminothermic method from BaO.
Physical and chemical properties. In the form of simple substances, these are shiny silver-white metals, beryllium is hard (it can cut glass), but brittle, the rest are soft and ductile. A feature of beryllium is that it is covered in air with a thin oxide film that protects the metal from the action of oxygen even at high temperatures. Above 800°C, beryllium is oxidized, and at a temperature of 1200°C, metallic beryllium burns out, turning into a white BeO powder.
With an increase in the ordinal number of an element, the density, melting and boiling points increase. The electronegativity of the elements of this group is different. For Be, it is quite high (ze = 1.57), which determines the amphoteric character of its compounds.
All metals in free form are less reactive than alkali metals, but are quite active (they are also stored under kerosene in sealed vessels, and calcium is usually in tightly closed metal cans).
Interaction with simple substances. The chemical activity of metals increases in a subgroup from top to bottom with an increase in the serial number.
In air, they are oxidized to form oxides of MeO, while strontium and barium, when heated in air to ~500°C, form peroxides of Me0 2 , which at higher temperatures decompose into oxide and oxygen. Interaction with simple substances is presented in the diagram:
All metals actively interact with non-metals: with oxygen they form MeO oxides (Me \u003d Be - Ra), with halogens - halides, for example MeCl 2 chlorides, with hydrogen - MeU 2 hydrides, with sulfur - MeS sulfides, with nitrogen - Me 3 nitrides N 2, with carbon - carbides (acetylenides) MeS 2, etc.
With metals, they form eutectic mixtures, solid solutions, and intermetallic compounds. Beryllium with some d-elements forms beryllides - compounds of variable composition MeBe 12 (Me = Ti, Nb, Ta, Mo), MeBe tl (Me = Nb, Ta), characterized by high melting points and resistance to oxidation when heated to 1200-1600°C.
Attitude towards water, acids and alkalis. Beryllium in air is covered with an oxide film, which causes its reduced chemical activity and prevents its interaction with water. It exhibits amphoteric properties, reacts with acids and alkalis with the release of hydrogen. In this case, salts of cationic and anionic types are formed:
Concentrated cold HN0 3 and H 2 S0 4 passivate beryllium.
Magnesium, like beryllium, is resistant to water. It interacts with cold water very slowly, since the resulting Mg (OH) 2 is poorly soluble; when heated, the reaction is accelerated by the dissolution of Mg(OII) 2 . It dissolves very vigorously in acids. The exceptions are HF and H 3 P0 4 , which form sparingly soluble compounds with it. Magnesium, unlike beryllium, does not interact with alkalis.
Calcium subgroup metals (alkaline earth) react with water and dilute hydrochloric and sulfuric acids to release hydrogen and form the corresponding hydroxides and salts:
With alkalis, similarly to magnesium, they do not interact. Properties of compounds of elements of the subgroup HA. Compounds with oxygen. Beryllium oxide and hydroxide are amphoteric in nature, the rest are basic. The bases that are readily soluble in water are Sr (OH) 2 and Ba (OH) 2, they are classified as alkalis.
BeO oxide is refractory (δmelt = 2530°C), has an increased thermal conductivity and, after preliminary calcination at 400°C, chemical inertness. It has an amphoteric character, interacts during fusion with both acidic and basic oxides, as well as with acids and alkalis when heated, forming, respectively, beryllium salts and beryllates:
The corresponding beryllium hydroxide Be (OH) 2 behaves in a similar way - not dissolving in water, it is soluble in both acids and alkalis:
For its precipitation, not alkali is used, but a weak base - ammonium hydroxide:
The hydrolysis of beryllium salts proceeds with the formation of precipitates of poorly soluble basic salts, for example:
Only alkali metal beryllates are soluble.
MgO oxide (burnt magnesia) - refractory (? pl = 2800°C) inert substance. In technology, it is obtained by thermal decomposition of carbonate:
Fine-crystalline MgO, on the contrary, is chemically active and is the main oxide. It interacts with water, absorbs CO 2 , easily dissolves in acids.
oxides alkaline earth metals receive in the laboratory thermal decomposition of the corresponding carbonates or nitrates:
in industry - thermal decomposition of natural carbonates. Oxides vigorously interact with water, forming strong bases, which are second only to alkalis in strength. In the series Be (OH) 2 -> Ca (OH) 2 -> Sr (OH) 2 -> Ba (OH) 2, the basic nature of hydroxides, their solubility and thermal stability are enhanced. All of them vigorously interact with acids to form the corresponding salts:
Unlike beryllium salts, water-soluble salts of alkaline earth metals and magnesium do not undergo cation hydrolysis.
Solubility in water of salts of elements of the PA-subgroup is different. Well soluble are chlorides, bromides, iodides, sulfides (Ca - Ba), nitrates, nitrites (Mg - Ba). Slightly soluble and practically insoluble - fluorides (Mg - Ba), sulfates (Ca - Ba), orthophosphates, carbonates, silicates.
Compounds with hydrogen and non-metals. MeH 2 hydrides, Me 3 N 2 nitrides, MeS 2 carbides (acetylides) are unstable, decompose with water to form the corresponding hydroxides and hydrogen or hydrogen compounds of non-metals:
Application. Beryllium easily forms alloys with many metals, giving them greater hardness, strength, heat resistance and corrosion resistance. Beryllium bronzes (copper alloys with 1-3% beryllium) have unique properties. Unlike pure beryllium, they lend themselves well to machining, for example, they can be used to make strips as thin as 0.1 mm. The tensile strength of these bronzes is greater than that of many alloy steels. As they age, their strength increases. They are non-magnetic, have high electrical and thermal conductivity. Due to this complex of properties, they are widely used in aviation and space technology. In nuclear reactors, beryllium is used as a neutron moderator and reflector. In a mixture with radium preparations, it serves as a source of neutrons produced by the action of alpha particles on Be:
BeO is used as a chemically resistant and refractory material for the manufacture of crucibles and special ceramics.
Magnesium is mainly used for the production of "ultralight" alloys, in metallothermy - for the production of Ti, Zr, V, U, etc. The most important magnesium alloy is electron(3-10% A1 2 0 3, 2-3% Zn, the rest Mg), which, due to its strength and low density (1.8 g / cm 3), is used in rocketry and aircraft engineering. Mixtures of magnesium powder with oxidizing agents are used for lighting and incendiary rockets, projectiles, in photographic and lighting technology. Burnt magnesia MgO is used in the production of magnesium, as a filler in the production of rubber, for the purification of petroleum products, in the production of refractories, building materials, etc.
MgCl 2 chloride is used to obtain magnesium, in the production of magnesian cement, which is obtained by mixing pre-calcined MgO with a 30% aqueous solution of MgCl 2 . This mixture gradually turns into a white solid mass, resistant to acids and alkalis.
The main application of metal calcium - reducing agent in the production of many transition metals, uranium, rare earth elements (REE).
Calcium carbide CaC 2 - for the production of acetylene, CaO - in the production of bleach, Ca (OH) 2, CaC0 3, CaS0 4 H 2 0 - in construction. Ca(OH) 2 ( milk of lime, slaked lime) used as a cheap soluble base. Natural calcium compounds are widely used in the production of binders for mortars, for the manufacture of concrete, building parts and structures. The binders are cements, gypsum materials, lime and others. Gypsum materials are, first of all, burnt gypsum, or alabaster, - hydrate of composition 2CaS0 4 H 2 0. Main application strontium And barium - getters in electrovacuum devices. Solution Ba(OH) 2 ( barite water, caustic barite) - laboratory reagent for a qualitative reaction to CO 2 . Barium titanate (BaTi0 3) is the main component of dielectrics, piezo- and ferroelectrics.
element toxicity. All beryllium compounds are toxic! The dust of beryllium and its compounds is especially dangerous. Strontium and barium, being nerve and muscle poisons, also have general toxicity. Barium compounds cause inflammatory diseases of the brain. The toxicity of barium salts is highly dependent on their solubility. Practically insoluble barium sulfate (pure) is not poisonous, but soluble salts: chloride, nitrate, barium acetate, etc. are highly toxic (0.2-0.5 g of barium chloride cause poisoning, lethal dose - 0.8-0.9 G). The toxic effect of strontium salts is similar to that of barium salts. Oxides of calcium and other alkaline earth metals in the form of dust irritate the mucous membranes, and in contact with the skin causes severe burns. Strontium oxide acts similarly to calcium oxide, but much stronger. Alkaline earth metal salts cause skin diseases.
